1. Field of the Invention
This invention relates to a process for preparing cyclohexanol and cyclohexanone, in particular, to a process for preparing cyclohexanol and cyclohexanone by selectively oxidizing cyclohexane with Fe/Pd catalyst in a flow of hydrogen and oxygen gases in the mixture of acetone and acetic acid.
Cyclohexanol and cyclohexanone are available as intermediates for synthesizing nylon-6 and nylon-6,6 and generally produced by oxidation of cyclohexane on an industrial scale. But the conventional processes of preparing cyclohexanol and cyclohexanone have some deficiencies that these processes require a condition of high temperature over 150.degree. C. and high pressure over 8 atm and its conversion is as low as 4%. Further, the product selectivity cannot exceed 80% because various decomposed oxidation-products of cyclohexane are produced from these reactions.
Because of the above problems, continuous researches on more effective and selective processes for preparing cyclohexanol and cyclohexanone have been conducted. For example, European patent appln. No. 83-87,924 discloses a process for preparing alcohol or ketones by oxidizing parraffinic hydrocarbons in a reaction system which employs iron catalyst, hydrogen sulfide, acetic acid, pyridine solvent and oxygen. But the resulting mixture shows poor separation and recovery of catalyst and products and especially, a large amount of pyridine is used compared to the amount of reaction product. Therefore, the problems of economical deficience and toxicity were raised.
As another example, in Japanese patent unexamined publication 85-92,236, cyclohexanone was acquired by adding oxygen to cyclohexene but there remains a problem that the manufacture of cyclohexene is more difficult that that of cyclohexane.
Additionally, the inventors of this invention discloses in U.S. Pat. No. 5,208,392 a method for preparing cyclohexanol and cyclohexanone with about 3.about.7% yields with no byproducts, by the oxidation of cyclohexane in hydrogen and oxygen gases with Fe/Pd catalyst in acetone solvent.
This invention is an improvement of U.S. Pat. No. 5,208,392 in that the activity and the stability of catalyst are improved through ligand binding with iron catalyst by using the solvent mixture of acetone and acetic acid instead of pure acetone solvent. As the result, yields of cyclohexanol and cyclohexanone increased significantly compared with those of U.S. Pat. No. 5,208,392. And especially, the more reaction time is extended and the more yields increase greatly up to about 4.about.12% because the deactiviation of catalyst is reduced. Moreover, there is little or nothing of byproducts during the oxidation of cyclohexane and the recovering and reusing of solid Fe/Pd catalyst is very easy.